Electrostatic precipitators can collect either solid or liquid particulates very efficiently, particularly those smaller than 2 microns. In a precipitator, particles are charged in an electric field and move to a surface of opposite charge where they are deposited. Precipitators exhibit low pressure drops, low consumption of electrical power, and low operating costs. Moreover, they recover particulates in agglomerated form, rendering them more easily collectible in case of reentrainment.
Electrostatic precipitators are often used for removing dust from gases of low conductivity, such as flue gas, gaseous effluents from cement or gypsum calcination operations or refinery process streams. Single-stage precipitation systems, commonly known as "Cotrell precipitators," are used for dust or mist collection in treating various industrial process gases. The collecting electrodes used may be parallel plates, screens, etc., or may be pipes, with the discharge electrodes being placed between the plates or within the pipes. U.S. Pat. No. 4,853,107 to Haddad et al. discloses the use of electrostatic precipitators for separating catalyst fines from the flue gas of fluidized catalytic cracking (FCC) units. Electrostatic precipitators, both single stage and two-stage, are further discussed in Kirk-Othmer, Encyclopedia of Chemical Technology, John Wiley & Sons, Third Ed., Vol. 1 at pp. 673-685 (1978).
One problem associated with electrostatic precipitators is the reentrainment of particulates in the flue gas when they are displaced from collecting electrodes, by application of sonic energy or mechanical rapping. In order to minimize reentrainment, the collecting surface should be struck by a force of proper intensity to snap the dust cake formed on the collecting electrode loose and allow it to slide down in cake form into a dust hopper from which it can be collected. Such reentrainment has been further minimized by adding baffles to collecting electrode plates in order to keep the bulk of the flue gas away from the dust cake and provide a quiescent zone for dust to slide downward during rapping. However, such arrangements can impair the flow of gas resulting in unacceptable pressure drop. U.S. Pat. No. 4,029,485 to Siwersson et al. teaches an electrostatic gas cleaner having collecting electrodes mounted concentrically around the discharge electrodes which collecting electrodes are rotated in order to throw off collected particles within a casing not influenced by the gas flow between discharge and collecting electrodes.
All of the above-mentioned publications are incorporated herein by reference.